As revealed by Sky Sports earlier this week West Ham are thought to be leading the chase for Valencia following his impressive performances for Ecuador at the World Cup.
The 25-year-old scored all three of Ecuador's goals at the finals in Brazil as they crashed out in the group stages.
The likes of Porto, Everton, Newcastle and Stoke have all been linked with a move for Valencia, but West Ham are thought to be in pole position to land the powerful forward.
Martinez has confirmed he is close to agreeing a deal with a mystery English club for Valencia and that it will be a club record deal if it goes through.
"There are various offers for Enner Valencia, the strongest and closest to what the player and us are demanding is from a club from England. We are making huge steps to finalize the negotiation," Martinez told Ecuagol.
"We are seeking the possibility that is convenient for him and the club and that he is sold for the price that we like for everything the Mexican league is worth.
"We want to keep a percentage of the player in case he is sold in the future to another big team in Europe."
When asked about the price, Martinez added:
"I won't talk about prices, but if he is sold, it will be the highest transfer fee ever in Mexican football football, otherwise he won't be sold," added Martinez
Martinez admitted it hurts him to lose Valencia, but conceded that the club could not stand in Valencia's way to further his career.
"It hurts me, I don't want to sell him and neither does the manager or the fans but we can't go against the career the kid aspires to, first because of the salary that they pay there, five times bigger (than what he is paid here) and he also wants to prove himself in the best league in the world, which is the Premier League and that will make Pachuca very proud as we will be sending other players to Europe," concluded Martinez.